Where Vp is the
voltage in the primary coil.Vs is the voltage in the secondarycoil.Np is the number of turns of
wire on the primary coil.Ns is the
number of turns of wire on the
secondarycoil.

There are two points to remember.

1.
Transformers only work with alternating
current.
Using direct
current will create a magnetic
field in the core
but it will not be a changing magnetic field
and so novoltage will be induced in the secondarycoil.

2.
Using a stepup transformer to increase the voltage
does not give you something for nothing. As the voltagegoes up, the current goes
down by the same
proportion.
The power equation shows
that the
overall powerremains the same,

In reality, the outputpower is always less than the
inputpower
because the changing magnetic field in
the core
creates currents (called eddy currents) which heat the core.
This heat is then lost to the environment, it is wasted
energy.